More and more data is recently transmitted over a wireless communication network due to appearance of various devices, such as smartphones or tablet PCs, which require machine-to-machine (M2M) communication and transmission of a large amount of data. More interest is oriented toward carrier aggregation and cognitive radio technologies that enable effective use of a broader frequency bandwidth to satisfy transmission of a large amount of data and multi-antenna technologies and multi-base station cooperative technologies that may raise data capacity in a limited frequency range.
Further, wireless communication networks have been evolving in such a manner that the density of nodes to which a user may gain access increases. Here, the “nodes” occasionally mean antennas or antenna groups which are spaced apart at a predetermined distance in a distributed antenna system (DAS), but are not limited to such concept, and may be expanded in meaning. That is, a node may be a pico-cell base station (PeNB), a home base station (HeNB), an RRH (remote radio head), an RRU (remote radio unit), or a relay. When having higher density of nodes, the wireless communication system may show higher system performance thanks to inter-node cooperation.
In other words, rather than when operating as an independent base station (Base Station (BS), Advanced BS (ABS), Node-B (NB), eNode-B (eNB), Access Point (AP), etc.) without cooperation from another node, when the transmission/reception is managed by a control station to thereby operate as an antenna or antenna group in a cell, each node may exhibit much higher system performance. Hereinafter, a wireless communication system including a plurality of nodes is referred to as multi-node system.
Not only when defined as an antenna group having a predetermined interval, but also when defined as an antenna group that has nothing to do with the interval, the nodes may apply. For example, it can be seen that a base station including cross polarized antennas is constituted of a node having an H-pol antenna and a node having a V-pol antenna.
In the multi-node system, different nodes from each other for each terminal may transmit a signal to the terminal, and a plurality of nodes may be set. At this time, different reference signals for each node may be transmitted. In such case, the terminal may measure a channel state between each node and the terminal based on the plurality of reference signals and may periodically or aperiodically feed back channel state information.